"The Remembering Bath"

Stochastic resetting — periodically returning a particle to its starting position — creates stationary states even for processes that would otherwise diffuse indefinitely. In a simple viscous fluid, the math is clean: exponential tails on the position distribution, a well-defined steady state, no complications.

A viscoelastic bath changes everything. The medium has memory. When the particle resets, the bath doesn’t. The stress history accumulated during the particle’s excursion persists in the surrounding fluid, encoded in the slow relaxation of polymer chains or the rearrangement of a colloidal network. The particle returns to the origin; the environment remembers where it was.

This memory manifests in the stationary distribution. In a Markovian (memoryless) bath, resetting produces exponential tails — the probability of finding the particle far from the origin decays exponentially. In a viscoelastic bath with strong memory, the tails become non-exponential. The distribution fattens because the residual stress from past excursions biases the particle’s subsequent motion, creating correlations that survive the reset.

The mean first-passage time inherits the same complication. In memoryless environments, an optimal resetting rate exists — too frequent and the particle never explores far enough, too rare and it wanders too long. In a viscoelastic bath, the optimization landscape deforms because the bath’s memory creates an effective force that depends on the entire resetting history.

The result inverts the usual intuition about resetting as a simplification. Resetting is normally studied because it converts complicated non-equilibrium dynamics into tractable stationary problems. But when the environment itself carries memory, the reset doesn’t fully reset the system. The particle’s state is restored; the bath’s state is not.

The environment is the memory. Resetting the system without resetting its context is not resetting at all.


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